Skip to main content
scroll to top
For Immediate Release
June 4, 2021


Update: Cyanobacteria Blooms Observed Across Several New Hampshire Lakes

It is very common to see cyanobacteria blooms, or green surface scums, this time of year. Heavy rain can sometimes introduce nutrients that can spark the growth of cyanobacteria. These cells grow in the water column of lakes and rise to the surface, getting caught in the surface tension. Ultimately these blooms are carried and dispersed around the lake, driven by wind, currents and weather.

Cyanobacteria bloom on Swains Lake in Barrington.NHDES is following up on several reports. There is currently an advisory for Robinson Pond in Hudson, Swains Lake in Barrington, Webster Lake in Franklin and Strafford Town Beach on Bow Lake. Cyanobacteria blooms have also been observed (and have begun to dissipate) on Island Pond in Stoddard and Province Lake in Effingham. Other waterbodies with reports of cyanobacteria include Highland Lake in Stoddard, Tucker Pond in Salisbury, and Clough Pond in Loudon.

Surface blooms can rapidly change and accumulate in various locations around a waterbody. Please continue to monitor your individual shorelines for changing conditions. NHDES advises lake users to avoid contact with the water in areas experiencing elevated cyanobacteria cell conditions, also known as a bloom. NHDES also advises pet owners to keep their pets out of any waters that have a cyanobacteria bloom.

Cyanobacteria are natural components of water bodies worldwide, though blooms and surface scums may form when excess nutrients are available to the water.  Some cyanobacteria produce toxins that are stored within the cells and released upon cell death. Toxins can cause both acute and chronic health effects that range in severity.  Acute health effects include irritation of skin and mucous membranes, tingling, numbness, nausea, vomiting, seizures and diarrhea. Chronic effects may include liver and central nervous system damage. Be cautious of lake water that has a surface scum, changes colors, or appears to have green streaks or blue-green flecks aggregating along the shore.  

Cyanobacteria alerts have been locally shared. NHDES has collected several samples across the state and will report any updates.

Visit the NHDES Beach Program website for photos and more information about cyanobacteria.
View updates on cyanobacteria advisories.
Follow the Beaches twitter feed.

If you notice anything resembling cyanobacteria, please refrain from wading, swimming, or drinking the water. Keep all pets out of the water and contact NHDES immediately. Please call NHDES to report a cyanobacteria bloom at (603) 848-8094 or email [email protected].